Why isn't salt required to compare whether password is correct in bcrypt?

Question

I would like to use node.js bcrypt to hash passwords before storing them in the database.

This link provides the documentation. https://github.com/kelektiv/node.bcrypt.js

Here is an example on hashing the password.

var bcrypt = require('bcrypt');
const saltRounds = 10;
const myPlaintextPassword = 's0/\/\P4$$w0rD';

var salt = bcrypt.genSaltSync(saltRounds);
var hash = bcrypt.hashSync(myPlaintextPassword, salt);
// Store hash in your password DB.

Here is the code to check the password.

// Load hash from your password DB.
bcrypt.compareSync(myPlaintextPassword, hash); // true

This is what I don't understand. In bcrypt.compareSync, why is there no parameter salt? Since the hash is generated from salt, why does comparing the plaintext password not involve the original salt used in hashing?

Answer 1

The salt is part of the string bcrypt stores in the database, see for instance the answer on Do I need to store the salt with bcrypt?